Method and device for monitoring the operation of a plain bearing

ABSTRACT

In a method of monitoring the operation of a plain bearing, a lubricant passage ( 15 ) of a bearing segment, this lubricating passage ( 15 ) being provided for jacking oil for example, is used during hydrodynamic operation of the plain bearing for extracting samples for a temperature measurement. For producing the measuring operation, a switch-over device ( 19 ) clears a flow path from the lubricant passage ( 15 ) into an outflow passage ( 23 ) in such a way that lubricant from the lubricating film ( 13 ) flows through the lubricant passage, the temperarature of this lubricant being determined by a temperature sensor ( 16, 18 ).

FIELD OF THE INVENTION

[0001] The present invention relates to a method of monitoring theoperation of a plain bearing according to the preamble of claim 1.Furthermore, the invention specifies a plain bearing which is especiallysuitable for implementing the invention.

DISCUSSION OF BACKGROUND

[0002] In a hydrostatic or hydrodynamic plain bearing, in which theactual support is carried out by a formed thin lubricating filmconsisting of a fluid (e.g. of an oil), a measurement of the temperatureof the lubricant in the lubricating film or a temperature measurement inthe adjacent sliding surfaces provides information about the state ofthe bearing and is therefore especially suitable for monitoring theoperation.

[0003] Thus it is known from EP 0 161 644, in a plain bearing for theearly detection of damage, to monitor the temperature in the region ofthe sliding layer in order to be able to take countermeasures in goodtime in the event of a noticeable increase in temperature. In this case,however, a change in the lubricant temperature is recorded with aconsiderable time delay and only indirectly. Even if the temperaturesensor were to be run directly to the surface or sliding surface, thetemperature of the bearing segment at best would be measured. Thelubricant or fluid temperature may locally be markedly above this, since90-97% of the heat generated in the fluid is dissipated by the fluiditself, that is to say past the temperature sensor; only 5% of the heatin terms of the order of magnitude is directed through the bearingsegment.

[0004] A direct measurement of the lubricant temperature in thelubricating film is not known in the prior art. The problem with thedirect measurement is that the film, for example in the case of oil aslubricant, is only 20 μm to about 200 μm thick, so that no probes can befitted. German Patent 883 984 specifies a bearing design for rollingmills which is supplied with an excess lubricant quantity for cooling,which is larger than the lubricant quantity which is to penetrate intothe lubricating gaps. The excess quantity is drawn off from fresh-oilchambers through a return line. German Patent 883 984 proposes toarrange a temperature sensor in this return line in order to determinethe temperature of the bearing surface. In this case, however, there ison the one hand the risk of the measurement being distorted by feedlubricant; on the other hand, the proposed measuring method can only beused in special bearings which are operated with excess oil.Furthermore, there are considerable uncertainties when drawingconclusions about the temperature in the bearing gap, since of coursethe measured medium does not originate explicitly from the bearing gap.

SUMMARY OF THE INVENTION

[0005] The object of the invention is to provide a method of monitoringthe temperature in a plain bearing working with a lubricating film, inparticular in a hydrodynamic plain bearing, which method avoids thedisadvantages of the prior art and in particular permits largely directand accurate monitoring of the lubricant temperature in the bearing gap,and requires the minimum possible modifications of existing bearings.Furthermore, a plain bearing is to be specified which, with littledesign outlay, permits as direct a measurement of the lubricanttemperature as possible and requires as far as possible no extensiveredesign of existing bearings or bearing segments.

[0006] Large plain bearings especially are often composed of a pluralityof bearing segments. Within the scope of the present invention, the ideabehind the invention is in no way affected by whether the invention isimplemented on a segmented plain bearing or on a plain bearing withoutsegments. Therefore the reference to one of the terms below alsoincludes the other, which is readily apparent to the person skilled inthe art.

[0007] The object is achieved by all the features of the independentclaims in their entirety. The essence of the invention consists inbringing the temperature sensor for the measurement directly intocontact with lubricant from the lubricating film by lubricant beingextracted from the lubricating film and by the temperature of theextracted lubricant being measured by the temperature sensor directlyafter the extraction. This is achieved by virtue of the fact that alubricant passage, such as a lubricant passage of a jacking-oilarrangement, which during the hydrodynamic operation of the bearing isnot required or is not permanently required for feeding lubricant, istemporarily or permanently operated by suitable switch-over means as anoutflow passage for a partial flow of the lubricant from the lubricatingfilm. In this case, the extraction flow, on the one hand, is to be keptso small that the pressure build-up in the lubricating film is notdisturbed; on the other hand, the extraction flow must be large enoughin order to keep a temperature change small which is due to heat lossesto the bearing segment, so that the temperature is “brought” from thelubricating film to the temperature sensor as far as possible withoutbeing distorted. The extraction flow is preferably set by acorrespondingly arranged, preferably adjustable, choke point. Forundisturbed functioning of the plain bearing, it is advantageous in thiscase if the quantity of lubricant extracted from the lubricating film iskept so small that the lubricating film does not change substantially;the extraction quantity is therefore preferably less than 5%, inparticular less than 2% or even markedly less than 1% of the entirelubricant quantity fed to the bearing for the hydrodynamic operation;nonetheless: the smaller the quantity extracted, the more sluggish isthe reaction of the measurement.

[0008] A further preferred configuration of the method according to theinvention is characterized by the fact that the pressure in thelubricant passage is measured while the method is being carried out. Therate of flow through a variable choke point is then varied as a functionof the measured pressure. Alternatively or additionally, the switch-overmeans may be activated as a function of the measured pressure in such away that, depending on the measured lubricant pressure, the feed of thelubricant to the lubricating film or the extraction of the lubricantfrom the lubricating film is released.

[0009] A plain bearing according to the invention or a plain bearingsegment is characterized by the fact that a lubricant passage opens outon a sliding surface of the plain bearing, the lubricant passage beingconnected at an end opposite this orifice to a suitable switch-overmeans, via which the lubricant passage can be optionally switched to afeed line for lubricant, for example from a high-pressure lubricatingsystem, in particular of a jacking-oil arrangement, and to an outflowline for lubricant. In addition, the term “plain bearing”, as describedabove, also relates to individual plain bearing segments. In particular,it is advantageous if a temperature sensor for determining the lubricanttemperature, in particular a thermocouple or a PT 100 temperaturesensor, extends into the lubricant passage. For a measurement which isas precise and as quick as possible, the temperature sensor, from thedesign point of view, is arranged as close to the orifice of thelubricant passage as possible. To limit and/or set the extraction flow,a preferably adjustable choke device is arranged in the outflow line forthe lubricant.

[0010] In a further embodiment of the plain bearing, apressure-measuring point is arranged in the lubricant passage, thesignal from this pressure-measuring point preferably being directed viaat least one controller to the switch-over means and/or to an adjustablechoke device arranged in the outflow line for lubricant and/or to alubricating or pressure oil system.

[0011] The bearing according to the invention is distinguished by itssimplicity, since lines which are present anyway internally and whichare not required for their actual use in all the operating states areused for extracting a measuring fluid from the bearing, the temperaturesensor being arranged in a protected manner in the interior of thebearing or of the bearing segment. Design changes to existing bearingsor bearing segments are restricted to a minimum and do not interferewith the functioning. In this respect, existing designs may also beretrofitted according to the invention without excessive outlay.

BRIEF DESCRIPTION OF THE FIGURES

[0012] The invention is to be explained in more detail below withreference to the drawing. The single FIGURE shows a bearing segmentaccording to the invention in a schematic sectional representation; thefollowing explanations and the drawing serve only for the betterunderstanding of the invention and are only to be understood in aninstructive sense and not in a restrictive sense.

WAYS OF IMPLEMENTING THE INVENTION

[0013] Reproduced in the FIGURE is a bearing segment of a hydrodynamicplain bearing having temperature monitoring of the lubricating filmaccording to a preferred embodiment of the invention. A hydrodynamicplain bearing 20 in the FIGURE consists of a plurality of bearingsegments, of which only the bearing segment 11 is shown, which isprovided with a high-pressure lubricating system, for example of ajacking-oil arrangement, which is only partly indicated by the pump 28.Such bearing segments are arranged in particular in a bottom region of abearing. At low speeds of a shaft mounted in the bearing, a sufficienthydrodynamic lubricating film still cannot be built up. Such ajacking-oil arrangement is therefore used especially in the case ofheavily weighted bearings. Before the shaft is started up, lubricant,when the shaft is at rest, is forced by the high-pressure pump 28through the lubricant passage 15 into the bearing gap (not shown) and,in the ideal case, lifts the load to be carried completely from thesliding surface 12. After that, the shaft is successively set in motion.In this case, the orifice 14 of the lubricant passage is designed insuch a way that a lubricating film 13 wetting the bearing surface ascompletely as possible is built up in such a way that the emergencyrunning properties of a sliding layer 12 are not called for. Withincreasing speed of a shaft mounted in a hydrodynamic plain bearing, asufficiently high pressure builds up in the lubricating gap so that thebearing load can be carried solely by the hydrodynamic lubricating filmformed. This pressure frequently exceeds that which can be reasonablyapplied by a pump; a check valve 22 is therefore arranged in the feedline 21 for the lubricant; and furthermore, for example, apressure-relief device known per se could be arranged between the checkvalve 22 and the pump 28 in order to protect the pump from overload.During hydrodynamic operation of the bearing, the lubricant passage 15is therefore no longer required for its actual task. According to theinvention, a sample flow from the bearing gap is therefore admitted tothe lubricant passage. To this end, a switch-over valve 19 is arrangedat the lubricant passage 15, by means of which switch-over valve 19 thelubricant passage can be optionally switched to the lubricant feed line21 and an outflow line 23. If hydrodynamic operation is thereforeensured, the switch-over valve 19 is thus switched in such a way thatlubricant flows. off from the lubricating film 13 into the outflow line23. A temperature sensor 16 is arranged in such a way that it extendswith its actual measuring point 18 into the lubricant passage; in thiscase, this measuring point is preferably arranged as close to theorifice 14 of the lubricant passage 15 as possible from the design pointof view. In this way, the temperature sensor 16 determines thetemperature of the lubricant coming from the lubricating film 13, thistemperature, in the design selected, corresponding very accurately tothe temperature of the lubricating film 13. The extracted quantity inthis case must be small enough in order to not effectively disturb thelubricating film; on the other hand, it should be large enough for themeasurement to be effected in a relevant and precise manner. Theextracted quantity is set via a, preferably variable, choke device 24arranged in the outflow line 23. In a simple case, the position of theswitch-over valve 19 is controlled, for example, via the shaft speed insuch a way that, up to a first speed, lubricant flows from the feed line21 into the lubricant passage 15, and, above this speed, the flow pathfrom the lubricant passage to the outflow line 23 is cleared. In theexample shown, another control means has been selected. Apressure-measuring point 17 is arranged in the lubricant passage 15. Apressure measured there is used as a reference variable for a number ofcontrol interventions. In this case, the pressure in the lubricatingpassage, in the embodiment shown, is controlled in three controldomains. In a first control domain, which is placed within a lowestpressure range, a pressure signal from the measuring point 17 acts viathe controller 27 on the high-pressure lubricating system or the pump28, respectively. In the process, the flow path from the feed line 21 tothe lubricant passage 15 is cleared in the switch-over valve. In asecond control domain, the switch-over valve 19 is actuated via thecontroller 26 as a function of the measured pressure, the controller 26preferably being a two-point controller: the flow path from thelubricant passage 15 to the outflow line 23 is cleared above a firstpressure limit value; the conduction of the lubricant is thus switchedover to the measuring operation. A reversed switching operation iseffected at a second pressure limit value which is lower than the firstpressure limit value. By the hysteresis of the switching points which isthus implemented, uncontrolled switching back and forth is avoided.During the measuring operation, the choke device 24 is set within alowest pressure range to a predetermined minimum rate of flow. The thirdcontrol domain is effective at a higher pressure, and, via thecontroller 25, the pressure in the lubricant passage 15 is set via therate of flow through the choke point 24.

[0014] The configuration according to the invention and the methodaccording to the invention result in sensitive and exact monitoring ofthe operation of the plain bearing. Incipient bearing damage, which ispreceded by a rise in the lubricant temperature in the lubricating film13, is immediately recorded.

List of Designations

[0015]11 Bearing segment

[0016]12 Sliding layer

[0017]13 Lubricating film

[0018]14 Orifice, lubricant outlet

[0019]15 Lubricant passage

[0020]16 Temperature sensor

[0021]17 Pressure-measuring point, pressure sensor

[0022]18 Measuring point of the temperature sensor

[0023]19 Switch-over means, switch-over valve

[0024]20 Plain bearing

[0025]21 Feed line

[0026]22 Check valve

[0027]23 Outflow line

[0028]24 Choke device

[0029]25 Controller

[0030]26 Controller

[0031]27 Controller

[0032]28 Lubricating system, high-pressure lubricating system,jacking-oil arrangement, pump

What is claimed is:
 1. A method of monitoring the operation of a plainbearing (20), in which plain bearing, in a first operating state, afirst lubricant quantity is fed from a lubricant passage (15) to alubricating film (13), characterized in that, in a second operatingstate, a second lubricant quantity flows off from the lubricating film(13) through the lubricant passage (15), and the temperature of thesecond lubricant quantity is measured.
 2. The method as claimed in claim1, characterized in that the lubricant passage (15) is connected via aswitch-over means (19) to a feed line (21) for the first lubricantquantity and to an outflow line (23) for the second lubricant quantity,and in that, to measure the lubricant temperature, the switch-over value(19) is switched over in such a way that the second lubricant quantityflows off into the outflow line (23).
 3. The method as claimed in eitherof the preceding claims, characterized in that the second lubricantquantity is set by a choke device (24).
 4. The method as claimed inclaim 3, characterized in that the rate of flow through the choke device(24) is set as a function of a measured pressure in the lubricantpassage (15).
 5. The method as claimed in claim 2, characterized in thatthe switch-over means (19) is activated as a function of a measuredpressure in the feed passage (15) in such a way that the feed line (21)for the first lubricant quantity is cleared below a first limit valueand the outflow line (23) for the second lubricant quantity is clearedabove a second limit value.
 6. A plain bearing or a plain bearingsegment, having a sliding surface (12) and a lubricant passage (15)opening out in the sliding surface, characterized in that the lubricantpassage (15) is optionally connected via a switch-over means (19) to afeed line (21) for lubricant and to an outflow line (23) for lubricant.7. The plain bearing or plain bearing segment as claimed in claim 6,characterized in that a temperature sensor (16, 18) extends into thelubricant passage (15).
 8. The plain bearing or plain bearing segment asclaimed in either of claims 6 and 7, characterized in that an inparticular adjustable choke device (24) is arranged in the outflow line(23) for lubricant.
 9. The plain bearing or plain bearing segment asclaimed in one of claims 6 to 8, characterized in that apressure-measuring point (17) is arranged in the lubricant passage (15).10. The plain bearing or plain bearing segment as claimed in claim 9,characterized in that a signal is directed from the pressure-measuringpoint (17) via at least one controller (25, 26, 27) to the switch-overmeans (19) and/or to an adjustable choke device (24) arranged in theoutflow line (23) for lubricant and/or to a lubricating system (28).